A recent development in the field of electro-mechanics has been the miniaturization of various mechanical devices. These "micro mechanical" devices are manufactured using integrated circuit techniques. They often have components made by depositing a thin metal film. The film may be etched or otherwise shaped so as to give the component its desired structure.
When these thin metal components are a moving mechanism, such as a hinge, creep and sagging can be a problem. The size and mechanical considerations constrain the films from which these components are made to thicknesses and linear dimensions that allow the components to distort a significant fraction of their dimensions.
One approach to solving the distortion problem is to manufacture components from "memory metals". A characteristic of these metals is that they can undergo phase changes while in the solid state. One class of these phase changes is the transition between an austenite phase and a martensite phase. As a result, the solid exhibits two phases with different structures and physical properties. Mechanical distortion that occurs during the martensite phase can be reversed. An excellent discussion of nickel titanium, a type of memory metal, is set out in an article by Gisser, et al., "Nickel-Titanium Memory Metal", Journal of Chemical Education, Vol. 71, No. 4 (April 1994).
The use of memory metals for coil spring micro-actuators is described in an article by Ikuta, et al., "Mathematical Model and Experimental Verification of Shape Memory Alloy for Designing Micro Actuator", Proc. of the IEEE Conf. on Micro Electro Mechanical Systems, Nara, Japan (1991), pp. 103-108. The article describes a coil spring made from a shape memory alloy, for the purpose of preventing fatigue from compressive and tensile forces.